Re: Presentation Syntax - why?
Danny - since this document isn't a Last Call document (and isn't
currently on the path to becoming one), I will take the liberty of
interacting without a Working Group mandate. So these comments can be
considered my own opinion, not those of the group.
Frankly, I don't understand your point of view as raised in this message.
Most of the work I do in RDF is done using N3, because I find it easier to
use. My tools translate that N3 to RDF/XML, which is then used directly or
turned into triples by some other tool. WOuld you argue against use of N3
or RDF/XML or Ntriples because they are all variants on using "pure" RDF
triples (as are stored into the underlying RDF DB).
Many thanks for taking the time to respond.
I am not arguing against the XML Presentation Syntax at this point, merely
trying to discover what it adds. However I probably would argue against
another variant of NTriples that was very similar in syntax and represented
the same data as NTriples, but had just enough changes that meant it
couldn't be used with existing tools.
OWL (Full) is a vocabulary extension to RDF (c.f [1] - my slides from
the W3C track at WWW). It can be written directly in RDF/XML, it can be
written in N3, and now, thanks to the document you are complaining about,
there is an XML presentation that more directly corresponds to the abstract
syntax we use in proving the semantic properties of OWL (and particularly
the OWL DL profile of OWL). This presentation syntax comes with an XSLT
that maps it into RDF/XML [2], and this is how we would expect it to
interact with other OWL (and RDF Core and RDFS) tools. Thus,this syntax is
just another way to produce OWL documents for people who have a different
tool set.
Again I wasn't actually complaining about the document. I'm curious to
know to which tool set you are referring, but can happily accept that it may
be easier to work with DL-style constructs using the new syntax.
XML and RDF have different models, but many XML schemas can be mapped
into perfectly reasonable RDF/XML, and this is one of them. It guarantees
that documents that validate against this schema, and go through this XSLT,
end up as legal RDF documents consistent with the OWL DL profile. This is
why we stress its role as a presentation syntax - like N3 or Ntriples it is
another way to look at RDF documents
Other people are working on UML presentation syntax for OWL (the OMG has
released a call to produce a two-way mapping between UML-2 and OWL), a
graphical presentation syntax, a prolog front-end.
The difference in this case is that there already is a comparatively
widely deployed XML syntax for RDF.
All of these things lead to further adoption of OWL (and thus RDF) and
I do not understand why you think they could be bad things.
I don't think and didn't say they are bad things. I was suggesting that it
seemed like a dichotomy had appeared, with the RDF M&S (revised) on one side
and the OWL AS&S on the other. Each now with their own XML serialization.
Ok, it may be possible to map between the two, but this approach doesn't
really conjure up a layered architecture like that of TimBL's famous
diagram.
I also must state that I am personally upset at your charge that the
activity of this working group is in any way mysterious. Guus and Ihave
worked very hard as chairs, spurred on by Dan Connolly as team contact, to
make sure that everything the WG did was in public, and that every decision
we made was open to anyone who wanted to track it. The issue about whether
to have an XML presentation has been in our publicly available issues list
since Oct 2002 [4]. The WG decided to have this document as an "appendix"
in Dec 02, but later decided a separate note made more sense. Further, our
entire mail archive is open to the public, and if you search on "XML
presentation syntax" you will find close to 150 messages dating back to May
2002 -- so you've had over a year to "study the chrystalline structure of
our DNA -- we've made it damned easy to do!
Please accept my apologies for any implication I may have made that things
might be happening in any untoward fashion. But I did spend time searching
relevant web pages, including the list archives before posting the mail - I
found a lot of posts relating to implementation issues (the crystalline
structure), and after a while I gave up looking for the original motivations
and decided to send a mail instead. The reason for creating the syntax given
in the issue list by the way is "would be useful" - hardly a double helix.
-Jim Hendler
p.s. I might also suggest you read the article Bijan Parsia and I wrote in
XML Journal [5], perhaps it can help clarify my position on why there is no
contradiction to having an XML presentation syntax for an RDF vocabulary.
A good article, and a point of view with which in general I agree (see my
SSR spec [6] for evidence). But I have yet to really get to the bottom of
why it was felt necessary to create *another* XML syntax for the *same*
material. I'm not saying that there is anything necessarily wrong with this,
but without further explanation it appears strange. If the reason is that an
XML schema-compatible syntax was thought desirable, fine. If the reason was
that it made life easier for folks coming from a DL viewpoint, fine. Either
of these motivations would still beg the question as to why a Presentation
Profile or whatever of RDF/XML wasn't created for the purpose (maintaining
direct tool compatibility), especially given the energetic defence this
syntax receives against those who suggest it's hard to use. If the real
reason was *because it can be done* then also, fair enough. I'm just
curious.
C heers,
Danny.
[1] http://www.w3.org/2003/Talks/0522-webont-hendler/
[2] http://www.w3.org/TR/2003/NOTE-owl-xmlsyntax-20030611/owlxml2rdf.xsl
[3]
http://www.w3.org/2001/sw/WebOnt/webont-issues.html#I5.17-XML-presentation-s
yntax
[4]
http://www.w3.org/2001/sw/WebOnt/webont-issues.html#I5.17-XML-presentation-s
yntax
[5]
http://www.mindswap.org/papers/XML-J-Oct2002.pdf
[6] http://purl.org/stuff/ssr
--
Professor James Hendler hendler@cs.umd.edu
Director, Semantic Web and Agent Technologies 301-405-2696
Maryland Information and Network Dynamics Lab. 301-405-6707 (Fax)
Univ of Maryland, College Park, MD 20742 *** 240-277-3388 (Cell)
http://www.cs.umd.edu/users/hendler *** NOTE CHANGED CELL NUMBER ***